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May the States Block Illegal Immigration?

May the States Block Illegal Immigration?

This essay first appeared on January 30, 2025 in Ford Forum, sponsored by the Gerald R. Ford Presidential Foundation at the University of Michigan.

If federal authorities fail to stem illegal immigration, may the states do so?

The answer to that question depends on whether the adoption of the Constitution left states with the authority to control their own borders. This, in turn, is tied up with the question of whether states may wage defensive war—and, if so, when.

For some writers, the answer is easy: Only the federal government may control immigration. In their view, moreover, states may not wage war without permission from Congress. As one of them opined, under the Constitution “war was to be a national business.”

Similarly, three federal appeals courts have said that, although the Constitution allows the states to respond if “invaded,” only an organized military attack by a foreign power qualifies as an “invasion.” Unauthorized immigration—no matter how extensive or harmful—does not.

In 2023, Massachusetts scholar Andrew T. Hyman and I began to investigate these issues. Amazingly, we found that they had never been the subject of a comprehensive published study. Claims such as the foregoing were based on simple speculation, backed by very little serious research. Sometimes they were even contradicted by the Constitution’s plain text.

Our conclusions were published early last year in the British Journal of American Legal Studies.

The Historical Background

Modern Americans commonly think of the Declaration of Independence as announcing the emergence of a new nation. But the operative words of the Declaration actually proclaimed the creation of thirteen new nations: “Free and Independent States . . [that] have full power to levy war, conclude peace, contract alliances, establish commerce, and do all other acts and things which independent states may of right do.” The Treaty of Paris—by which the British Crown recognized American independence—acknowledged the existence of these thirteen new sovereignties.

The Articles of Confederation, adopted in 1781, did not change this. Although the Articles sometimes are characterized as our “first constitution,” they were not a constitution in the modern sense. According to Eighteenth-Century dictionaries, the word “confederation” denoted merely a treaty or alliance among sovereign governments, and this is confirmed by the Articles themselves and by how the Founders discussed them. In fact, the Articles resembled the North Atlantic Treaty Organization (NATO) more than they resembled a government. The Confederation Congress occupied a position similar to that of NATO’s North Atlantic Council.

Under the Articles, the states granted Congress significant war powers. But they also retained extensive war powers of their own. And they retained nearly exclusive control over their borders.

Only after the federal government commenced operation in the spring of 1789 could one say the states were not fully sovereign. Even then, three states continued for a time as independent nations: North Carolina did not join the Union until late in the year, Rhode Island stayed out until 1790, and Vermont—which had been an independent republic since 1777—finally joined in 1791. Of course, three subsequently-admitted states also have been independent nations: Texas, California, and Hawai’i.

This pre-constitutional state sovereignty is relevant because it is a key to understanding how the Constitution altered it.

The Constitutional Background: Immigration

A fundamental axiom of U.S. constitutional law is that the Constitution granted the new federal government only certain enumerated powers. The Constitution left the remainder with the states. The states did not receive this remainder from the Constitution; it was part of their residual sovereignty.

Moreover, unless the Constitution specified, directly or indirectly, that the federal government’s jurisdiction over a subject was exclusive, the states could continue to regulate the matter as well. They enjoyed concurrent (although subordinate) jurisdiction over it.

The Constitution granted Congress authority to control immigration (Article I, Section 8, Clause 10). Notably, however, the Constitution did not make that grant exclusive. On the contrary, Article I, Section 9, Clause 1 implicitly acknowledged continued state authority over immigration. It provided in part, “The Migration or Importation of such Persons as any of the States now existing shall think proper to admit, shall not be prohibited by the Congress prior to [1808] . . . .” The records of the Constitution’s ratification confirm that although “Importation” referred to the slave trade, “Migration” referred to the voluntary movement of free people.

By this clause, Congress could not limit state control over immigration until 1808. After that, it could. But state power over immigration didn’t go away: It became concurrent with, and subordinate to, congressional authority.

The Constitutional Background: War Powers

The Constitution’s treatment of war powers is more complicated, and grasping it requires some background in Eighteenth-Century international law. Part of this background is the difference between offensive and defensive war.

The details appear in our article, but the short version is this: The Constitution granted the federal government power to wage both offensive and defensive war. But while the federal power to enter into offensive operations was nearly exclusive, the states’ authority to wage defensive war was very broad—in fact, even broader than it had been under the Articles of Confederation.

The Constitution’s text confirmed this. Article I, Section 10, Clause 1 provided in part: “No State shall, without the Consent of Congress . . . engage in War, unless actually invaded, or in such imminent Danger as will not admit of delay.” If we put this in positive terms, it means that states may engage in defensive war when faced with invasion or the imminent threat of invasion.

The Meaning of “Invade”

The words “invade” and “invasion” show up in four separate parts of the Constitution. In each case, the word triggers a power or obligation to wage a defensive war.

But what does the Constitution mean by “invade” and “invasion?” To answer this question, we investigated how those words were used in Eighteenth-Century political discourse. We examined thirteen (and, subsequently, a 14th) Founding Era dictionaries—looking not only at the meaning of “invade” and “invasion” but at the meaning of the words used to define them. We followed up by scouring databases of Eighteenth-Century political and legal writings.

The results were very clear: The constitutional terms “invade” and “invasion” not only included formal military incursions. They also included cross-border attacks by hostes humani generis (“enemies of the human race”)—that is, transnational criminal gangs such as the Mexican drug and human-trafficking cartels. Most tellingly, “invade” and “invasion” included even peaceable incursions by unauthorized immigrants.

For example, before the Constitution was adopted, Connecticut settlers moved into Pennsylvania’s Wyoming Valley. They relied on Connecticut land claims, but their immigration violated Pennsylvania law. Both Benjamin Franklin and the Pennsylvania legislature referred to these peaceful but unauthorized immigrants as “invaders.”

Is State Action “Nullification?”

“Nullification” is a state resolution declaring a federal law void. One commentator has claimed that by ordering state defense against illegal immigration in defiance of the Biden administration, the governor of Texas was trying to “nullify” federal law.

We found this claim to be groundless. Texas actually was trying to enforce federal law—something that under the Constitution’s Supremacy Clause (Article VI, Clause 2) it has every right to do.

But this raised a more difficult question: Suppose Congress changed the law to allow unlimited foreign immigration into Texas. (There was a hint of this in the administration’s abortive consideration of a “remain in Texas” policy.) Could Congress forbid the state from protecting its border?

The answer is “Probably not.” The Supreme Court has ruled repeatedly that even otherwise-constitutional federal laws cannot impair crucial aspects of state sovereignty. Congress may not dictate the location of a state capital, compel a state to accept title to hazardous waste, or require state officials to enforce a federal law.

Those aspects of sovereignty are less important than border control, which Justice Antonin Scalia described in a 2012 case as the “defining characteristic” of sovereignty.  It is, therefore, unlikely the court would force a state to accept unlimited immigration against its will.

Conclusion

Eighteenth-century international law texts identified a wide range of options states could use when defending themselves. Exploring all of them is beyond the scope of this essay. However, one option—erecting physical barriers to entry—was recently at issue in a federal appeals court case: United States v. Abbott.

Texas floated barriers in the Rio Grande to prevent migrant river crossings. The Biden administration sought removal of the barriers, claiming that Texas could not employ its war powers without congressional permission and that, even if it could, placing barriers in a navigable stream violated federal law.

The court gave short shrift to the argument that Texas needed federal permission to erect barriers. Rather, it focused on whether that part of the Rio Grande was navigable, and found that it was not.

Judge James C. Ho concurred in an opinion that reinforced some of our own findings: “A sovereign isn’t a sovereign,” he wrote, “if it can’t defend itself against invasion . . . And the States did not forfeit this sovereign prerogative when they joined the Union . . . Nothing in [the Constitution] prevents a State from defending itself if it is ‘actually invaded,’ whether or not the United States is also able and willing to protect the State.”

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Rob Natelson
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